In an interactive numerical control device, when cutting a region which must be cut several times by a turning tool, the tool is usually manufactured with an edge on only one side thereof Accordingly, the cutting is made always in one direction, and the tool is operated so that it is returned to a machining start point by a rapid traverse after the cutting.
FIG. 4 shows an example of a passage of a conventional machining program. In FIG. 4, numerals 1 and 3 denote a workpiece and a tool for one-way cutting, respectively. The axes of abscissa and ordinate represent the coordinate Z- and X-axes, respectively. As shown in FIG. 4, a passage for the tool 3 is made in the order P1, P2, P3, P4, P5, P6. In the tool passage, the full line indicates cutting, and the broken line indicates a rapid traverse.
When using this machining passage, however, if the tool is a turning tool capable of multi-directional cutting, the tool is often moved unnecessarily, thus prolonging the machining time and requiring a long NC statement.